In the electronics industry, the continuing goal has been to reduce the size of electronic devices, such as camcorders and portable telephones, while increasing performance and speed. Integrated circuit packages for complex electronic systems typically have a large number of interconnected integrated circuit chips. The integrated circuit chips are usually made from a semiconductor material such as silicon or gallium arsenide. The various semiconductor devices on the integrated circuit chips are formed in various layers on the chips using photolithographic techniques. After manufacture, the integrated circuit chips are typically incorporated into packages that are then mounted on printed circuit wiring boards.
Integrated circuit chip packages typically have numerous external pins that are mechanically attached by solder or a variety of other known techniques to conductor patterns on the printed circuit wiring boards.
Typically, the packages in which these integrated circuit semiconductor chips are mounted include a substrate or other chip mounting device. One example of such a substrate is a leadframe. High performance leadframes typically are multi-layer structures including power, ground, and signal layers on separate planes.
Leadframes also typically include an area on which a semiconductor integrated circuit chip is mounted and in which a number of power, ground, and/or signal leads is attached to the semiconductor integrated circuit chip. In particular, the power, ground, and/or signal leads of the leadframe are connected electrically to power, ground, and/or signal sites on the integrated circuit semiconductor chip.
Semiconductor integrated circuit chips may be attached to the leadframe using adhesive or any other appropriate techniques for attaching such chips to a leadframe. Techniques commonly known to those skilled in the art for attaching such chips to a leadframe, for example, include soldering.
Once the integrated circuit chip(s) are attached mechanically and electrically to the leadframe, the leadframe may be enclosed or encapsulated in a protective enclosure. Such enclosures may include encapsulation in a plastic or a multi-part housing made of plastic, ceramic, or metal. The enclosure may protect the leadframe and the attached chip from physical, electrical, moisture, and/or chemical damage.
The leadframe and attached chip(s) may then be mounted on, for example, a circuit board or card along with other leadframes or devices. The circuit board or card may then be incorporated into a wide variety of devices such as computers, cellular telephones, automobiles, appliances, and so forth.
Typical known leadframes that include a number of layers on different planes are complex and expensive to produce. Multiple planes have been incorporated into the design of many leadframes as a solution to accommodate the high density of leads needed for the highly complex integrated circuits typically used today.
In many such multiple plane designs, each plane has a single function, such as ground, power, or signal. The separation of the functions in the different planes is to help electrically isolate the various planes in order to reduce electrical interference, such as noise, from one plane to another.
Unfortunately, even when the layers are built up using known techniques, such multi-layer leadframes, although functionally effective, are very complex and often are not cost effective.
Another problem with these multi-layer leadframes is that the ground plane preferably must be in a different layer from the semiconductor chip mounting structure, such as a die attach or mounting paddle. Single and double downsetting and upsetting methods have been developed to accomplish this. However, these methods cause mechanical stress on the ground plane and result in ground plane distortion or warp.
The ground plane distortion or warp prevents the ground plane from sitting flat on a wire bonding heater block and causes bouncing of the ground plane during the wire bonding process, resulting in poor ground bonding integrity.
Solutions to problems of this sort have been long sought, but have long eluded those skilled in the art.